E. Chandran et Ml. Nibert, PROTEASE CLEAVAGE OF REOVIRUS CAPSID PROTEIN MU-1 MU-1C IS BLOCKED BYALKYL SULFATE DETERGENTS, YIELDING A NEW-TYPE OF INFECTIOUS SUBVIRIONPARTICLE/, Journal of virology, 72(1), 1998, pp. 467-475
Mammalian reovirus virions undergo partial disassembly of the outer ca
psid upon exposure to proteases in vitro, producing infectious subviri
on particles (ISVPs) that lack protein sigma 3 and contain protein mu
1/mu 1C as endoprotease-generated fragments mu 1 delta/delta and phi.
ISVPs are thought to be required for two early steps in reovirus infec
tion: membrane penetration and activation of the particle-bound viral
transcriptase complexes. Genetic and biochemical evidence implicates o
uter-capsid protein yl in both these steps. To determine whether the c
leavage of mu 1/mu 1C is relevant to the unique properties of ISVPs, w
e analyzed the properties of novel subvirion particles that lacked sig
ma 3 yet retained mu 1/mu 1C in an uncleaved but cleavable form. These
detergent-plus-protease subvirion particles (dpSVPs) were produced by
treating virions with chymotrypsin in the presence of micelle-forming
concentrations of alkyl sulfate detergents. Infections with dpSVPs in
murine L or canine MDCK cells provided evidence that the cleavage of
mu 1/mu 1C during viral entry into these cells is dispensable for reov
irus infection. Additionally, dpSVPs behaved like ISVPs in their capac
ity to permeabilize lipid bilayers and to undergo transcriptase activa
tion in vitro, supporting the conclusion that cleavage of mu 1/mu 1C t
o mu 1 delta/delta and phi during viral entry is not required for eith
er membrane penetration or transcriptase activation in cells. The capa
city of alkyl sulfate detergents to inhibit the cleavage of mu 1/mu 1C
in a reversible fashion suggests a specific association between virus
particle and detergent micelles that may mimic virus particle-phospho
lipid membrane interactions during reovirus entry into cells.